mardi 13 octobre 2015

Scientists using NASA’s Hubble Space Telescope have produced new maps of Jupiter – the first in a series of annual portraits of the solar system’s outer planets.

Jupiter in 4k Ultra HD

Video above: This new portrait of Jupiter was produced from observations made using NASA’s Hubble Space Telescope. Video Credits: NASA/ESA/Goddard/UCBerkeley/JPL-Caltech/STScI.

Collecting these yearly images – essentially the planetary version of annual school picture days for children – will help current and future scientists see how these giant worlds change over time. The observations are designed to capture a broad range of features, including winds, clouds, storms and atmospheric chemistry.

Already, the Jupiter images have revealed a rare wave just north of the planet’s equator and a unique filamentary feature in the core of the Great Red Spot not seen previously.

“Every time we look at Jupiter, we get tantalizing hints that something really exciting is going on,” said Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This time is no exception.”

Simon and her colleagues produced two global maps of Jupiter from observations made using Hubble’s high-performance Wide Field Camera 3. The two maps represent nearly back-to-back rotations of the planet, making it possible to determine the speeds of Jupiter’s winds. The findings are described in an Astrophysical Journal paper, available online.

The new images confirm that the Great Red Spot continues to shrink and become more circular, as it has been doing for years. The long axis of this characteristic storm is about 150 miles (240 kilometers) shorter now than it was in 2014. Recently, the storm had been shrinking at a faster-than-usual rate, but the latest change is consistent with the long-term trend.

The Great Red Spot remains more orange than red these days, and its core, which typically has more intense color, is less distinct than it used to be. An unusual wispy filament is seen, spanning almost the entire width of the vortex. This filamentary streamer rotates and twists throughout the 10-hour span of the Great Red Spot image sequence, getting distorted by winds blowing at 330 miles per hour (150 meters per second) or even greater speeds.

In Jupiter’s North Equatorial Belt, the researchers found an elusive wave that had been spotted on the planet only once before, decades earlier, by Voyager 2. In those images, the wave is barely visible, and nothing like it was seen again, until the current wave was found traveling at about 16 degrees north latitude, in a region dotted with cyclones and anticyclones. Similar waves – called baroclinic waves – sometimes appear in Earth’s atmosphere where cyclones are forming.

(Click on the image for enlarge)

Image above: In Jupiter’s North Equatorial Belt, scientists spotted a rare wave that had been seen there only once before. It is similar to a wave that sometimes occurs in Earth’s atmosphere when cyclones are forming. This false-color close-up of Jupiter shows cyclones (arrows) and the wave (vertical lines). Image Credits: NASA/ESA/Goddard/UCBerkeley/JPL-Caltech/STScI.

“Until now, we thought the wave seen by Voyager 2 might have been a fluke,” said co-author Glenn Orton of NASA’s Jet Propulsion Laboratory in Pasadena, California. “As it turns out, it’s just rare!”

The wave may originate in a clear layer beneath the clouds, only becoming visible when it propagates up into the cloud deck, according to the researchers. That idea is supported by the spacing between the wave crests.

In addition to Jupiter, the researchers have observed Neptune and Uranus, and maps of those planets also will be placed in the public archive. Saturn will be added to the series later. Hubble will dedicate time each year to this special set of observations, called the Outer Planet Atmospheres Legacy program.

Image above: The movement of Jupiter’s clouds can be seen by comparing the first map to the second one. Zooming in on the Great Red Spot at blue (left) and red (right) wavelengths reveals a unique filamentary feature not previously seen. Image Credits: NASA/ESA/Goddard/UCBerkeley/JPL-Caltech/STScI.

“The long-term value of the Outer Planet Atmospheres Legacy program is really exciting,” said co-author Michael H. Wong of the University of California, Berkeley. “The collection of maps that we will build up over time will not only help scientists understand the atmospheres of our giant planets, but also the atmospheres of planets being discovered around other stars, and Earth’s atmosphere and oceans, too.”

The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. NASA's Goddard Space Flight
Center in Greenbelt, Maryland, manages the telescope. The Space
Telescope Science Institute (STScI) in Baltimore, Maryland, conducts
Hubble science operations. STScI is operated for NASA by the Association
of Universities for Research in Astronomy, in Washington.